Bleaching



Patented Feb. 16, 1937 BLEACHING Wilhelm Hirschkind, Berkeley, Calif., assignor to Great Western Electro-Chemical Company, a corporation of California No Drawing.

Serial No. 23,850.

Original application May 28, 1935,

Divided and this application July 27, 1936, Serial No. 92,848

9 Claims.

, This case is a division of my application Serial No. 23,850 filed May 28,1935.

This invention relates to the treatment of groundwood or mechanical pulp and more par- 5 ticularly to the manufacture of products from such pulp as newsprint, specialty papers, boards,

etc. Groundwood'pul-p, as is well known in the art, is produced by the mechanical disintegration of wood so that the pulp contains all of the 10 lignins and resins, in fact all of the constituents of the wood. In view of all these compounds being present, the bleaching of groundwood pulp and the production of light paper therefrom presents a difiicult problem. In my prior patent Re- 15 issue No. 19,470 of February 19, 1935, I have disclosed the use of hydrosulphites as a bleaching agent for this purpose. I have now found that groundwood pulp can be lightened more effectively and permanently by the use of various mem bers of a group of compounds known as sul phoxylates.

The materials disclosed herein are more advantagously employed than those in my application Serial No. 23,850, filed May 28, 1935. In 25 that case I have disclosed the use of addition products of hydrosulfurous acid. These are satisfactory but the materials of this case are less corrosive under the same conditions and give a better brightening or bleach. Representatives 30 of these compounds are given in the following:

Sodium formaldehyde sulphoxylate .\'aHSO -CH=O Zine formaldehyde sulphoxylaie ZnSO2-CB2O SOCHzOHO 85 Zinc formaldehyde sulphoxylate Zn SOCHQOHO I do not limit'myself to these representatives since, for instance, the formaldehyde in this combination can be substituted by any other aldehydes such as acetaldehyde or any ketone as acetone, or other ketones and the metal, sodium or zinc can be replaced by other metals as for instance potassium. calcium, magnesium or by theammonium radical. The outstanding characteristics of these compounds are that they are very stable at ordinary temperature and that their bleaching efiect is exerted only at high temperatures (above 100 F.) up tothe boiling point 50 of water. g

' In utilizing the process of my invention. I either add the compound as a solid, in form of a solution to the material to be bleached or else I form the compound in situ in the material undergoing bleaching. Thus I have bleached groundwood pulp by adding to the hot pulp at about 180 F. zinc formaldehyde sulfoxylate in small amounts. The pulp reduced quickly in color and finished with a considerably lighter and more permanent color than one bleached under similar conditions with hydrosulphite alone or with a hydrosulphite addition compound. I have also successfully bleached groundwood pulp by forming the sulfoxylate directly therein by methods well known for manufacture .of this material. Zinc formal- 10 dehyde sulfoxylate can be produced readily from zinc hydrosulphite and formaldehyde by the addition of zinc dust in an acid aqueous medium, or else the addition compound, zinc hydrosulphite formaldehyde, can be treated with zinc dust in an acid aqueous medium. Another method is by treating hydrosulphite with formaldehyde in the presence of an alkali or by treating the addition compound zinc hydrosulphite formaldehyde with an alkali such as causticsoda, caustic potash or ammonia. There are also other combinations possible such as starting out from alkali sulphitesor from S02 and treating with zinc dust, thereby forming hydrosulphite as the intermediate product.

In the manufacture of groundwood pulp, good use can be made of the heat generated in the grinding operation by adding the sulfoxylate directly to the water which is used .in the grinder although the heat source is not-limited to this.

-The temperature in the grinder is usually above 120, usually 140 F. and may go as high as 200 F. Under these conditions the bleaching process is usually completed in a short time. Depending on the type of pulp and the quality of bleaching agent used it may or may not beadvantageous to add a washing step. The treatment to be used may be the sameas that disclosed in my pending application, Serial-No. 755,929 filed December 4, 1934.

As above indicated high temperature is essential in bleaching with these compounds and by utilizing the heat of the grinding operation this temperature is obtained without any additional cost although the pulp can be heated if desired artificially. The better results obtained with these compounds over inorganic hydrosulfites, especially the greater permanency of the color, easily offset the heating costs so that the bleaching step does not have to be confined to the grinding operation but can be practiced at any point in the flow of the pulp up to the paper machine proper whereat the pulp is hot.

The bleach occurs quickly, usually in less than half an hour. After the bleach, depending on the material, the pulp may be washed or directly converted into paper. It is to be pointed out that a pulp bleached with a sulphoxylate is many times more stable than one bleached with a hydrosulfite. For example, two batches of the same pulp were bleached at the same time, one with a hydrosulfite and the other with a sulfoxylate. After bleaching they were permitted to remain exposed to the air in their aqueous suspension. The hydrosulfite bleached pulp darkened quickly while the sulfoxylate bleached pulp did not darken until after nearly a week had elapsed.

With some wood pulpsit is advantageous to wash after bleaching while with others it is not.

useful wherever a quick lightening of color is.

desired at. lost cost. The materials useful in accordance with this invention are more satisfactory for high temperature bleaching than inorganic hydrosulfites inasmuch as they show a very marked increase in color lightening. This makes them useful in the production of news print from ground wood pulp as well as on press board products of board machines and specialty products. Since the bleach is very quick and yet effective it can be used to advantage on such products particularly as they have to be made at low unit cost becauseof the competition market existing. 7

It is an object of the present invention to provide a high temperature bleaching process for ground wood pulp.

Another object of the invention is to providean improved process for the manufacture of a product of a light color from ground wood pulp.

The invention possesses other objects and features of advantage, some of which, together with the foregoing, will appear hereinafter- One preferred operation is as follows:

Wood suitable for production of ground wood pulp is passed from storage to a grinder wherein it is mechanically disintegrated. As is usual, the grinder is showered with water and this water stream carries'the wood pulp away while cooling the grinder. The pulp stream has a v temperature leaving the grinder of between 100 F.-212 F. and usually between 140 F:

180 F. This heat is supplied by the work done in disintegrating the wood, the water shower cooling the grind stone and thus providing the heat for the pulp stream. The temperature of the incoming water stream-is usually between 32 F. and 80, F. At these temperatures the sulphoxylate is quite 'stable and exhibits little activity. It can therefore be manufactured and monium radical) and calcium sulfite, bisulfite, phosphate or borate. 1

After the sulphoxylate has been added to the pulp, a short time must be allowed for its action .to take place. This is usually only a matter of minutes, the sulphoxylate being added i anywhere in the operation. Since the sulphoxylate acts by reduction, the pulp, after its color has been lightened, will darken if the pH' is permitted to get much higher than 7.5 on the alkaline side. In connection with pH, the wood pulp is normally acid so that the pulp suspension is usually on the acid side initially. Under these circumstances, acidification need not be resorted to except when only a very alkaline water is available. Precautions against oxidation need not be taken ordinarily since the bleached pulp is quite stable, an unexpected result as well as an advantage over hydrosulphite bleaching which darkens readily on oxidation.

When the bleach has been completed, or while it is going on, the pulp may be subjected to compatible practices as screening, etc. The pulp can be washed after bleaching, if desired; for this a water slightly on the acid side is best used to avoid color reversion due to pH change and to secure the whitest paper. The bleached pulp with its coloring matter reduced can be run directly to the paper machine after its treatment and converted into paper. ing matter and diluents, as sulphite pulpycan be added as required.

The sulphoxylate 'added can be any of the usual sulphoxylates as a formaldehyde sulphoxylate and reaction products of an aldehyde with sulfoxylic acid or a salt thereof, particularly a metal 'salt as zinc or an alkali metal, sodium, potassium and ammonia, or one of the alkaline earths, calcium and magnesium. Various aldehydes can be used including acetaldehyde, formaldehyde and any of the other aldehydes or aldehyde compounds. The sulphoxylate can be formed virtually in situ by adding an aldehyde to water For this, sizing, colorcarrying a salt of sulfoxylic acid. Thus, zinc dust I and S02 can be added to the water. After a short time an aldehyde is added when the mixture is passed to the grinder shower. Instead of an aldehyde a ketone can be used. Both ketones and aldehydes form addition products so that any aldehyde or ketone can be used. The simplest formula for an aldehyde and a ketone is- R-C-R' where R is hydrogen for an aldehyde and any organic radical for a ketone wherein a carbon,

is bonded to the carbon in the formula. Any aldehydic or ketonic compound, aliphatic or cyclic, including carbocyclic as well as heterocyclic, within these formulas an be used as a. basis for forming the sulphoxylate.

The invention is applicable to any stock containing an appreciable percentage of ground wood pulp. An example of such a stock is news print stock which is made up of ground wood and sulphite pulps. The problem of lightening color of such a stock is present due to the presence of the ground wood in an appreciable percentage. Such mixed stocks are included and are contemplated in my process and are therefore within the scope of the claims.

I claim:

1. Bleaching ground wood pulp with an organic sulphoxylate at a temperature between 100" and 212= F.

2. Bleaching ground wood pulp with the addition product of a salt of sulfoxylic acid and an aldehyde at a temperature between 100 and 212 F.

3. Bleaching ground wood pulp with the addition product of asalt of sulfoxylic acid and a ketone at a temperature between 100 and 212 F.

4. Bleaching ground wood pulp at a temperature between l00-212 F. with the addition product of sulfoxylic acid and an organic compound of the formulawhere R is any organic radical and R is hydrogen or any organic radical.

5. Bleaching ground wood pulp at a tempera-' ture of about 140 F. with the addition product of sulfoxylic acid and an organic compound of of the formu1a--- 7. Bleaching ground Wood pulp at a tempera-- ture of about 140 F. with the addition product of sulfoxylic acid and an organic compound of the formula R-Ifi-R' where R is any organic radical and R is hydrogen or any organic radical, while maintaining said pulp at a pH substantially between 4.5 and 6.5 by addition of an inorganic alkaline salt effective to maintain said pH substantially between 4.5 and 6.5.

9. Bleaching ground wood pulp at a temperature of about 140 F. with the addition product of sulfoxylic acid and an organic compound of the formulawhere R is any organic radical and R is hydrogen or any organic radical, while, maintaining said pulp at a pH substantially between 4.5 and 6.5 by addition of an inorganic alkaline salt effective to maintain said pH substantially between 4.5 and 6.5.

I WILHELM HIRSCHKIND. 

